It has long been the practice to dismantle an internal combustion engine to determine the condition of its components. It is becoming increasingly desirable, however, to provide on-board diagnostic means for components which have a major impact on certain critical engine performance criteria. This is particularly true in the motor vehicle industry, where high precision in the control of fuel flow has become essential to various present and planned engine management features designed to meet increasingly strict emissions, performance, drivability, and maintenance objectives. Thus, it is now well known how to adjust the fuel flow to the cylinders of an engine to maintain desired fuel/air mixture ratio for meeting engine emission requirements by electronically controlling the actuation timing and duration of the engine's fuel injectors. Electronic fuel injector controls are presently available and in use, especially in the engines of more advanced motor vehicles. The control function may be incorporated into an electronic engine control (EEC) module performing a variety of engine control functions. In accordance with such known systems, the timing of injector actuation is controlled by the timing of the corresponding actuation signal sent by the control module. The duration of injector actuation, during which fuel is passed through the injector from a fuel rail or like fuel supply means, is controlled by the duration of the actuation signal from the control module, that is, by the pulse width of the signal.
Reliably controlling a fuel injector's fuel supply by controlling its actuation signal pulse width requires that the fuel injector be performing at or near its specified flow rate when open. A fuel injector may become clogged, however, over a period of use, potentially resulting in decreased engine efficiency, increased emission of undesirable combustion products, etc. Thus, in support of maintaining the efficacy of electronic engine management devices adapted to control air/fuel ratio by controlling the actuation of fuel injectors, it is now recognized to be highly desirable to provide means for detecting clogged or otherwise impaired fuel injectors. In particular, it is seen to be especially desirable to provide an on-board diagnostic system to periodically test an engine's fuel injectors during engine operation without requiring disassembly of the engine.